fairly numerous: Donegal-Derry etc. Ir. Ó Duibhidhir.(mod. Ó Duibhir). A sept of Tír Conaill also appearing as Deere. The name is cognate with O'Dwyer in the south. SI.

Dyer:

Quite numerous: Mayo, Belfast and scattered. An English occupational name but in Ireland usually for Mac Duibhir which commonly occurs as MacDyer. However the Dyers of Belfast may well be of English origin.